The present invention relates to a valve timing controlling apparatus for an internal combustion engine for making variable the opening/closing timing of an intake valve or exhaust valve of the internal combustion engine.
The valve timing controlling apparatus for an internal combustion engine adjusts the opening/closing timing of the intake valve or exhaust valve by changing the rotational phase of a cam shaft. As a result, it becomes possible to maximize the opening/closing timing of the intake valve or exhaust valve in correspondence with the operating state of the internal combustion engine, such as the load or the number of revolutions. Accordingly, it is possible to improve the fuel consumption, output, emission, and the like of the internal combustion engine in a wide range of operating states.
Various types of variable valve timing mechanisms for changing the valve timing in the above-described manner are present, and "Valve Opening/Closing Adjusting Apparatus" disclosed in Unexamined Japanese Patent Application No. Hei. 1-92504 can be cited as one example.
The variable valve timing mechanism of the type such as the one described in the aforementioned publication has a first rotating body for receiving a driving force from the crank shaft of the internal combustion engine and a second rotating body which rotates integrally with the cam shaft.
In a recessed portion formed in either one of the two rotating bodies, vanes formed in the other rotating body are disposed. As the recessed portion is partitioned by the vanes, a first hydraulic chamber and a second hydraulic chamber are formed on both sides of each vane.
By changing the oil pressure within the first arid second hydraulic chambers, the second rotating body is made to undergo relative rotation with respect to the first rotating body. As a result of this relative rotation, the relative angle of rotation of the second rotating body changes with respect to the first rotating body, with the result that the opening/closing timing of the intake or exhaust valve opened or closed by the cam shaft is changed.
More specifically, when the first rotating body and the second rotating body are made to undergo relative rotation, oil pressure is supplied to either of the first and second hydraulic chambers, and oil pressure is released from the other hydraulic chamber at the same time. On the basis of the pressure difference occurring in the supply and release of the oil pressure, the vanes move toward the hydraulic chamber side of low oil pressure, so that the first rotating body undergoes relative rotation with respect to the second rotating body.
When the aforementioned relative angle of rotation assumes an appropriate phase, oil pressure control is effected so that the oil pressures in the first and second hydraulic chambers become uniform. Consequently, the movement of the vanes is restricted, and the relative angle of rotation is fixed.
The variable valve timing mechanism having the above-described construction is generally referred to as the "vane-type variable valve timing mechanism."
With this vane-type variable valve timing mechanism, there are cases where oil pressure cannot be sufficiently supplied to the variable valve timing mechanism such as at the time of starting the internal combustion engine, in which case the operation of the variable valve timing mechanism becomes unstable. To prevent this situation, as disclosed in Unexamined Japanese Patent Application No. Hei. 1-92504, a lock mechanism is provided to fix the relative rotation of the second rotating body with respect to the first rotating body when oil pressure supplied to the variable valve timing mechanism is insufficient such as at the time of starting the internal combustion engine.
As this lock mechanism, a mechanism is widely adopted which comprises a retaining hole formed in either of the two rotating bodies and a lock pin which is accommodated in an accommodating hole formed in the other rotating body and can be fitted into the retaining hole by being urged by a spring. The lock mechanism having such a lock pin is provided with a first unlocking hydraulic chamber and a second unlocking hydraulic chamber communicating with the aforementioned first and second hydraulic chambers. As oil pressure is supplied into these unlocking hydraulic chambers, the lock pin moves against the urging force of the spring, and is disengaged from the retaining hole, thereby canceling the locked state.
However, with the valve timing controlling apparatus having such a lock mechanism, at the time of changing over the direction of relative rotation of the second rotating body with respect to the first rotating body, there were cases where the cancellation of the locked state of the lock mechanism was impossible. Such a state in which unlocking is impossible hampers smooth valve timing control.
Hereafter, the mechanism of the occurrence of this problem will be described more specifically by citing an example.
Here, a description will be given of the case where a changeover is effected from the state in which the vanes are urged toward the second hydraulic chamber side by supplying oil pressure to the first hydraulic chamber to the state in which the vanes are urged toward the first hydraulic chamber side by supplying oil pressure to the second hydraulic chamber.
In an initial state, the interior of the first hydraulic chamber has been supplied with oil pressure, and oil pressure within the second hydraulic chamber has been released. At this time, on the basis of the oil pressure supplied into the first hydraulic chamber, the lock pin has been moved against the urging force of the spring, so that the lock mechanism is in the unlocked state.
In this state, if a control command is issued for changing over the direction of relative rotation, the oil pressure passage communicating with the first hydraulic chamber is opened, and the supply of oil pressure to the oil pressure passage communicating with the second hydraulic chamber is started at the same time. Consequently, the locked state of the lock mechanism is canceled on the basis of the release of oil pressure in the first hydraulic chamber and the first unlocking hydraulic chamber communicating with that hydraulic chamber is discharged, the supply of oil pressure into the second hydraulic chamber, and the supply of oil pressure into the second unlocking hydraulic chamber.
However, in reality the above-described series of operation is not carried out simultaneously, and is accompanied by slight time lags.
The release of the oil pressure in the first hydraulic chamber and the first unlocking hydraulic chamber communicating therewith is effected immediately.
Since the supply of oil pressure into the second hydraulic chamber is executed by lagging behind the release of the oil pressure from the first hydraulic chamber and the like since the flow of oil into the second hydraulic chamber is started after the oil pressure passage communicating with the second hydraulic chamber is first filled with the oil pressure.
The cancellation of the locked state of the lock mechanism on the basis of the supply of oil pressure to the second unlocking hydraulic chamber is executed by further lagging behind the aforementioned supply of oil pressure to the second hydraulic chamber.
Thus there is a time lag from the time there ceases to be no oil pressure in the first unlocking hydraulic chamber until the oil pressure in the second unlocking hydraulic chamber rises to a sufficient level. For this reason, at the time of directly changing over the direction of relative rotation of the second rotating body with respect to the first rotating body, unlocking is impossible even though temporarily.
Therefore, if the aforementioned direction of relative rotation is changed over at a relative angle of rotation at which the positions of the lock pin and the retaining hole are aligned with each other, the lock pin may be fitted into the retaining hole temporarily.
Furthermore, a situation can also occur in which the oil pressure within the second hydraulic chamber rises and the relative rotation of the second rotating body with respect to the first rotating body is started, before the oil pressure within the second unlocking hydraulic chamber rises and the lock pin is completely disengaged from the retaining hole. In such a case, since the lock pin is caught, the lock pin cannot be disengaged from the retaining hole, so that the relative rotation of the second rotating body with respect to the first rotating body cannot be effected smoothly.